Atomic-Level Study in the Structure and Its Instability of Metallic Glasses

Bulk metallic glasses (BMGs) possess a unique set of mechanical properties that make them attractive structural materials: yield strength > 2 GPa, fracture toughness ~20 MPa.m1/2 and elastic strain limit ~2%. BMGs can also be cast into intricate shapes which retain their dimensional integrity and require no further machining. Unfortunately, monolithic BMGs fail catastrophically under unconstrained loading by forming shear bands. To overcome this problem, BMG matrix composites with fiber and dendritic reinforcements were proposed. The former type includes metallic fibers of Ta, Mo and stainless steel. The latter composites develop precipitates during casting and are thus called in-situ composites. Here, the reinforcements form an interpenetrating dendritic structure and enhance the ductility of the composite. This study investigated the deformation behavior of these two types of BMG composites. Loading measurements were performed during neutron or high-energy X-ray diffraction to determine lattice strains in the crystalline reinforcements. The diffraction data were then combined with finite element and self-consistent modeling to deduce the behavior of the amorphous matrix, as well as to understand the effective deformation mechanisms in the composite. The deformation of the wire composites was studied using an integrated neutron diffraction and finite element (FE) approach. The FE model yielded a reasonable version of in-situ stress-strain plots for both reinforcements and the matrix. It was found that the reinforcements yielded first and started transferring load to the matrix which remained elastic throughout the whole loading experiment. The reinforcements were seen to possess yield strengths lower than their monolithic forms, likely due to annealing during processing. After optimizing material properties to fit experimental data, the FE model developed was reasonably successful in describing both the macroscopic composite deformation and the lattice strain evolution in the reinforcements. In the case of the in-situ composites, a detailed neutron and high energy X-ray diffraction study was conducted combined with a self-consistent deformation model. The compressive behavior of the composite and the second phase (in its monolithic form) were investigated. It was shown that the ductile second phase yields first upon loading the composite followed by multiple shear band formation in the BMG matrix, a process which enhances the ductility of the composite. It was also discovered that the mechanical properties of the reinforcements, and indirectly the composite, are highly variable and quite sensitive to processing conditions. This resulted from the unstable nature of the BCC beta phase reinforcements which tend to transform into an ordered phase leading to significant stiffening, but also loss of ductility. An additional heat treatment study confirmed this phase evolution. The overall conclusion of this study is that BMG composites with high ductility require reinforcements that yield first and induce multiple shear bands in the amorphous matrix, which in turn enhances the latter’s ductility. To also retain a high yield point, the reinforcements need to be stiff. These two properties can best be optimized in beta phase composites via a judicious combination of microstructure control and heat treatment.

半導體元件中介電材料的結構、電性、介電性質以及機械行為之理論分析與模擬研究

The efficiency of polymer extrusion processes can be severely limited by the occurrence of viscoelastic extrusion instabilities. In a para-aramid fibre spinning process, for example, a ?m-scale extrusion instability is responsible for the waste of tons of polymer per year. At present, a considerable amount of research literature is available on such viscoelastic extrusion instabilities. However, this literature largely applies to isotropic polymers, whereas the polymer solution that is used for the production of para-aramid fibres is liquid crystalline. Liquid crystalline polymers (LCPs) are anisotropic at rest, and their flow behaviour is known to deviate from that of other viscoelastic fluids. Therefore, more research was needed to characterise the extrusion instability in the para-aramid fibre spinning process. The work presented in this thesis deals, first, with the question to which extent the contraction flow of a nematic aramid solution is similar to contrac- tion flow of isotropic polymeric fluids. More specifically, we looked into the flow stability of nematic contraction flow, and its influence on the extruded aramid jet. Second, as a fibre spinning process typically involves the extrusion of around 1 000 closely spaced jets, the influence of the presence of neighbouring outlets on the behaviour of viscoelastic contraction flow is addressed. For the first part of the research, the aramid fibre spinning process was modelled by a 100 ?m deep 100:1 planar contraction flow with free outflow, which was designed to capture the essential features of the extrusion process. At a depth of 100 ?m the optically anisotropic aramid solution is sufficiently transparent to allow for flow visualisation, while at the same time the pressure drop over the geometry permits flow velocities that are realistic for fibre spinning, without damaging the glass flow cells in which the planar contraction geometries were etched. The contraction flow of a nematic aramid solution was compared with the behaviour of a PEG-PEO Boger fluid in the same geometry, using flow visualisation and Particle Image Velocimetry (PIV). It was shown that, under fibre spinning conditions, a nematic aramid solution shows viscoelastic vortex growth. Like in contraction flows of isotropic polymeric fluids, the vortex size in the aramid solution increases with increasing flow rate, and decreases when the contraction entrance is made more gradual (e.g. tapered, or rounded). The velocity field in the aramid solution was demonstrated to be characteristic of its shear-thinning behaviour. The influence of the defect structure in the aramid solution was visible in a wavy instability in the upstream channel, and in the occurrence of regions with a higher velocity than the surrounding flow, in the first minutes after starting the flow. The oscillation of the extruded jet was shown to be coupled to asymmetric velocity fluctuations in the upstream channel. Although no extrusion instability was encountered in the experiments, the existence of a relation between the jet behaviour and the upstream velocity field implies that the stability of the upstream velocity field is important for the stability of the jet. The similarity between the contraction flows of a nematic aramid solution and an isotropic viscoelastic fluid justifies the use of experiments with model fluids in the study of para-aramid fibre spinning. Therefore, the study of the influence of the presence of multiple outlets was carried out with a model fluid. Experiments using a PEG-PEO Boger fluid, and numerical simulations using a FENE-CR model (Finitely Extensible Non-linear Elastic, Chilcott-Rallinson closure), were performed in contraction geometries with one or three outlets, and a large or small distance between the outlets in the three-outlet geometries. The experiments and simulations show that in the three-outlet geometries, the curvature of the streamlines towards the outlets causes a horizontal pressure gradient in the upstream channel, resulting in the flow rate being distributed unequally over the outlets. Because the streamline curvature changes with increasing lip vortex size, the distribution of the flow rate over the outlets depends on the Weissenberg number of the flow. Furthermore, the vortex size was observed to decrease due to the presence of multiple outlets, with a smaller distance between the outlets leading to smaller lip vortices. This was demonstrated to result in a higher maximum elongation rate, a higher pressure drop over the geometry, and a decreased stability of the flow. The fluctuations in vortex height in what is classified here as unstable flow seems to lead to fluctuations in flow rate and outflow direction in the outlets. The results presented in this thesis are relevant for fibre spinning pro- cesses, but also for other production processes featuring multi-outlet extrusion of viscoelastic fluids. A logical next step would be to do experiments with a transparent model fluid in a more complex, three-dimensional extrusion geometry, to study extrusion instability in a multi-outlet geometry and to optimise the efficiency of such extrusion processes.

Metallic glasses (MGs) are a relatively new class of materials discovered in 1960 and lauded for its high strengths and superior elastic properties. Three major obstacles prevent their widespread use as engineering materials for nanotechnology and industry: 1) their lack of plasticity mechanisms for deformation beyond the elastic limit, 2) their disordered atomic structure, which prevents effective study of their structure-to-property relationships, and 3) their poor glass forming ability, which limits bulk metallic glasses to sizes on the order of centimeters. We focused on understanding the first two major challenges by observing the mechanical properties of nanoscale metallic glasses in order to gain insight into its atomic-level structure and deformation mechanisms. We found that anomalous stable plastic flow emerges in room-temperature MGs at the nanoscale in wires as little as ~100 nanometers wide regardless of fabrication route (ion-irradiated or not). To circumvent experimental challenges in characterizing the atomic-level structure, extensive molecular dynamics simulations were conducted using approximated (embedded atom method) potentials to probe the underlying processes that give rise to plasticity in nanowires. Simulated results showed that mechanisms of relaxation via the sample free surfaces contribute to tensile ductility in these nanowires. Continuing with characterizing nanoscale properties, we studied the fracture properties of nano-notched MGnanowires and the compressive response of MG nanolattices at cryogenic (~130 K) temperatures. We learned from these experiments that nanowires are sensitive to flaws when the (amorphous) microstructure does not contribute stress concentrations, and that nano-architected structures with MG nanoribbons are brittle at low temperatures except when elastic shell buckling mechanisms dominate at low ribbon thicknesses (~20 nm), which instead gives rise to fully recoverable nanostructures regardless of temperature. Finally, motivated by understanding structure-to-property relationships in MGs, we studied the disordered atomic structure using a combination of in-situ X-ray tomography and X-ray diffraction in a diamond anvil cell and molecular dynamics simulations. Synchrotron X-ray experiments showed the progression of the atomic-level structure (in momentum space) and macroscale volume under increasing hydrostatic pressures. Corresponding simulations provided information on the real space structure, and we found that the samples displayed fractal scaling (rd ∝ V, d < 3) at short length scales (< ~8 A), and exhibited a crossover to a homogeneous scaling (d = 3) at long length scales. We examined this underlying fractal structure of MGs with parallels to percolation clusters and discuss the implications of this structural analogy to MG properties and the glass transition phenomenon.

Microstructural control through heat treatments is one of the most important means of designing alloys to gain desired mechanical properties. As microstructural modifications in alloys are associated with creation of heterogeneities both in terms of chemistry (precipitates) and energy (defects such as dislocations, stacking fault and grain boundaries), they affect corrosion, especially the localized corrosion tendency of alloys. Contrary to this general wisdom, certain precipitation treatment in aluminium alloys has been found to impart high strength without sacrificing on uniform and localized corrosion resistance. Thus, the role of precipitates in influencing corrosion seems to be complex and needs a thorough understanding which may help to develop the guidelines for developing corrosion resistant structural alloys having high strength. In this study, three Al-based (Al-Ni-Y) metallic glasses with varying Ni content, namely Al87Ni9Y4, Al86Ni10Y4 and Al83Ni13Y4 were chosen as model alloy systems to investigate the mechanistic role of thermally-induced transformations or nanoscale precipitates on the corrosion properties. Annealing conditions (temperature and time) corresponding to different thermally-induced transformations such as structural relaxation, partial and full crystallization were selected based on the DSC thermograms. Synchrotron X-ray diffraction (XRD), nuclear magnetic resonance (NMR) spectroscopy and transmission electron microscope (TEM) were employed to characterize the structure of these metallic glasses before and after annealing. Surface characterization was done using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Potentiodynamic polarization and electrochemical impedance techniques were employed to study the corrosion behaviour of these glasses in a freely exposed 3.5 wt.% NaCl solution of pH 6.5. Annealing in all the three glasses below their respective first crystallization temperatures caused reduction in passive current density, although they were not found to undergo any structural relaxation which is in contrast with the published literature. The present study found that the Y segregation to the surface due to annealing causes reduction in passive current density. Y segregation has also been found to affect electrochemical corrosion behaviour of the glasses even in the crystallized state. Formation of FCC Al precipitates caused an increase in passive current density in all the conditions, but improves the pitting resistance. It is found that Y is the main element responsible for better corrosion resistance of Al-Ni-Y metallic glasses and since FCC Al precipitates is free of Y; these precipitates tend to dissolve faster than the matrix causing an increase in passive current density. On the contrary, stable pits are formed only when the pit size exceeds a critical level. Below the critical size pitting potential might raise as the precipitates may be covered with Y and/or Ni oxides. Enrichment of Ni and Y in the matrix in the immediate vicinity of the precipitate might help to cover the precipitates with more Ni and Y, and also suppress the pit growth beyond the pit. In contrasts to FCC Al precipitates, the intermetallic phases (Al3Ni and Al19Ni5Y3) rich in Y and Ni resist selective dissolution, but their formation results in Y and Ni lean matrix surrounding them and so they can induce galvanic corrosion. Therefore, as high temperature crystallization caused coarsening of FCC Al and increase in the volume fraction of Y and Ni containing intermetallic phases, and Y and Ni lean glassy matrix, the glasses lost their passivity. Thus, this study emphasizes the role of the size of the precipitates, chemistry of the precipitates and the chemistry of the surrounding matrix in electrochemical polarization tendency of the glasses. Based on these observations, a phenomenological model has been proposed to satisfactorily explain the change in the observed electrochemical behaviour (both the passive current density and pitting potential, which was not done in the published literature) of the alloys due to crystallization. Thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy of the Indian Institute of Technology Bombay, India and Monash University, Australia.

Bulk metallic glasses usually have very high yield strength, at least double that of ordinary commercially used crystalline materials, and high elastic strain limit, roughly 2% in tension or compression, due to their disordered atomic structure. Unfortunately, the Achilles heel of metallic glasses is their rather limited ductility and low resistance to the propagation of a crack especially in tension. Many research efforts have been devoted to understanding the deformation and fracture behavior of bulk metallic glasses. One interesting observation is that the properties of metallic glasses are well correlated with each other. The challenge is to understand these correlations, and to utilize such understanding to design novel glasses with good glass forming ability and mechanical toughness. Following the Cooperative Shear Model, we investigated the temperature, volume, and configurational dependence of elastic properties by constructing an effective tight-binding force field for a Cu-Zr binary alloy system, and carrying out molecular dynamics simulations. We determined the isothermal Equation of State in a wide range of temperatures and pressures. Pressure-induced cavitation was observed and negative pressure is critical for triggering cavitation. The cavitation barrier height was estimated from the classical nucleation theory. The intrinsic origin of cavitation and its connection to Poisson’s ratio or the ratio of G/B are investigated. The relationship to the deformation and fracture behavior of glasses is discussed. We designed several novel bulk metallic-glass-forming systems using the link between fragility, elastic properties, and glass forming ability as a guiding tool. The compositional dependence of thermal and elastic properties of Cu-Zr-Be ternary bulk-metallic-glass forming alloys was systematically studied. Lightweight Ti-based bulk amorphous structural metals with more than double the specific strength of conventional titanium alloys have been discovered. We report a novel class of bulk amorphous alloys with benchmark thermoplastic processability, having good glass forming ability, exceptional thermal stability, unexpectedly large Angell fragility number, and good mechanical toughness. Starting from the two binary bulk glass formers in the Cu-Zr system, we systematically investigated the compositional dependence of glass formation, thermal, elastic, and mechanical properties in the Cu-Zr-Ag ternary alloys.

The present thesis deals with molecular dynamics computer simulations of heterogeneities in copper–zirconium metallic glasses, ranging from intrinsic structural fluctuations to crystalline secondary phases. These heterogeneities define, on a microscopic scale, the properties of the glass, and an understanding of their nature and behaviour is required for deriving the proper structure–property relations. In terms of composite systems, we start with the amorphisation of copper nanolayers embedded in a metallic glass matrix. While copper is an fcc metal with a high propensity for crystallisation, amorphisation can in fact occur in such systems for thermodynamic reasons. This is due to interface effects, which are also known from heterogeneous interfaces in crystals or from grain boundary complexions, although in absence of lattice mismatch. In single-phase glasses, intrinsic heterogeneities are often discussed in terms of soft spots or geometrically unfavourable motifs (GUMs), which can be considered to be mechanically weaker, defective regions of the glass. We investigate the relation between these motifs and the boson peak, an anomaly in the vibrational spectrum of all glasses. We demonstrate a relation between the boson peak and soft spots by analysing various amorphous and partially amorphous samples as well as high-entropy alloys. Finally, we treat the plastic deformation of glasses, with and without crystalline secondary phases. We propose an explanation for the experimentally observed variations of propagation direction, composition, and density along a shear band. These variations of propagation direction are small in the case of single-phase glasses. A considerably greater influence on shear band propagation can be exerted by precipitates. We systematically investigate composites ranging from low crystalline volume fraction up to systems which resemble a nanocrystalline metal. In this context, we derive a mechanism map for composite systems and observe the breakdown of these mechanisms with increasing crystalline volume fraction during the transition towards the nanocrystalline state.

Stability of load carrying elements in glass The increasing demand in modern architecture for more slender and lighter structures requires the use of new construction materials. Glass, a material that has been used for a long time in windows as a filling material, has much to offer in this regard due to its very high compressive strength and transparency. For this reason, there is a growing trend to extend the use of glass sheets to load carrying elements such as columns, beams and panels. Due to their high slenderness and high compressive strength, such elements tend to fail because of instability (i.e. column buckling, lateral torsional buckling or plate buckling). At the moment little knowledge exists about the load carrying behaviour of glass structural elements, and existing design methods for other materials (i.e. steel) have been found to be unsuitable for direct transfer to the design of glass panels. With this in mind, the main objectives of the current thesis are: The study of the load carrying behaviour of glass elements which may fail due to lack of stability by means of laboratory tests and analytical and numerical models, as well as the study of the main influencing parameters. Discussion of possible design methods for glass elements which may fail due to lack of stability for the three main stability problems (column buckling, lateral torsional buckling and plate buckling) and proposition of possible aids for design such as buckling curves. The main influencing parameters (dispersion of the glass thickness, initial deformation) on the load carrying behaviour of glass elements which may fail due to lack of stability have been measured and are evaluated herein using statistical methods. The breakage stress, the thermal prestress and the effective tensile strength are defined and explained. Existing models to determine the tensile strength of glass are discussed. The column buckling behaviour of single layer and laminated safety glass is studied by means of column buckling tests, which are compared to analytical and numerical models. The models are used to study the influence of the main parameters, particularly the shear connection due to the interlayer (PVB) in laminated safety glass, on the load carrying behaviour and buckling strength of glass elements. On the basis of this study different possible design methods for column buckling of glass elements in compression are proposed and discussed. It is shown that a second order stress analysis is the most appropriate method for glass. As a further simplification, the cross section of a laminated safety glass structural element can be modelled as a monolithic cross section with an effective thickness. Analytical and numerical models for the lateral torsional buckling of glass beams are also verified by a comparison to test results. Along with a study of the main parameters, different methods to determine the lateral torsional buckling strength are discussed, and it is shown that buckling curves for lateral torsional buckling should be developed for glass beams using a slenderness ratio based on effective tensile strength. As a result of numerical simulations, recommendations for the future development of lateral torsional buckling curves of glass beams are given. The column buckling behaviour of single layer and laminated safety glass is also studied by means of column buckling tests, analytical and numerical models. It is shown that glass panels have a large post critical load carrying capacity but the way the loads are introduced into the panels, as well as the buckling shape, have an important influence on the plate buckling capacity. A design method with buckling curves using a slenderness ratio based on effective tensile strength seems applicable for the design of glass panels. As a result of numerical simulations, recommendations for the future development of plate buckling curves for plate glass elements under compression are given.

Owing to the unique properties, such as excellent mechanical performance, and nano-scale surface roughness, metallic glass can be applied in various novel fields. Meanwhile, the improvement of thermal stability and hardness is the common target in these applications. Minor alloying is an effective method to enhance the thermal and mechanical properties of metallic glasses. Different from elements used to be doped into metallic glass, the role nitrogen atoms play in metallic glass is quite distinct and critically important, owing to its strong electronegativity and small atomic radius. In this work, an alternative class of metallic glass is developed. By adding nitrogen into Zr-Cu-Al-Ag TFMG, the configuration energy of short range structure is greatly modified. From the viewpoint of thermal behavior, the evolution of Tg and elastic modulus with nitrogen could be well correlated, implying significant effect of nitrogen atoms on the potential energy landscape (PEL) of the TFMGs. Besides, more amounts of nitrogen addition lead to the increase of short range order structure in the amorphous matrix. That is, most metallic atoms are strongly attracted by nitrogen, forming the nitrogen-centered cluster, in which more energy is required to cause plastic deformation. On the other hand, a meta-stable state with lower energy is attained as indicated by the much higher Tx than normal Zr-based metallic glasses. However, the amorphicity region of nitrogen in Zr-Cu-Al-Ag metallic glass is not wide enough, restricting the enhancement amount of thermal and mechanical performances. By incorporating Ta firstly, the competing ZrN crystalline phase is destabilized, leading to the wider amorphicity region of nitrogen in Ta-Zr-Cu-Al-Ag TFMG. As a result, hardness over 10 GPa, Tg near 800 K, and supercool liquid region as wide as 112K is achieved in the nitrogen-doped Ta-Zr-Cu-Al-Ag TFMG.

The solidification microstructure in wedge-shaped castings of Cu-Ni-Ti-Zr glass forming alloys is investigated, while the composition was systematically varied. Near the critical thickness for glass formation, a spatially inhomogeneous dispersion of nanocrystals is observed, where spherical regions contain a much higher density of nanocrystals than the surrounding material. This microstructure is inconsistent with the prevalent theories for crystallization in metallic glasses, which predict a spatially uniform distribution of crystals. The spatial localization of the nucleation density is attributed to a recalescence instability. Linear stability analysis of the equations for heat flow coupled with crystal nucleation and growth reveals that at low temperature recalescence can occur locally, triggered by a small fluctuation in the early stages of the crystallization process, because in deeply undercooled liquids the nucleation rate increases with temperature. The localized recalescence events and their interaction accelerate crystallization; consequently they are important in determining the glass forming ability as well as the microstructure of these alloys. The composition dependence of the critical thickness for glass formation, determined from the observed microstructures, and in situ small angle scattering results indicate that the crystallization occurs in several steps, involving competing crystalline phases

The investigation of new glass compositions is crucial to expand the possible applications of glass, from the typical applications for building engineering, in the form of cast blocks or floated glass, to more advanced technologies, such as 3D-printed glass or glass to metal connections. Despite the intense research activity and new glass compositions being investigated every day, there has been little innovation or evolution in the composition of architectural glass. This is partially explained by the fact that a substantial part of glass research is not relevant to practical large-scale applications. This thesis is more concerned about the development of compositions with optimized properties than the studies of the short- and intermediate-range structure of a theoretical glass that would hardly find a practical application. Thus, these compositions are inexpensive and appropriate to mass production, utilizing conventional melting techniques. Since the high melting temperatures and the brittleness are two important drawbacks of glass, this work aims to improve both properties. The modification of the properties is achieved via changes in the composition of the glass, using compounds such as phosphorus pentoxide, aluminium oxide and boron oxide. Then, the choice of different glass formers and modifiers contributes to the development of compositions with lower melting and glass transition temperatures. The reduction of the melting temperature allows a saving of energy during the manufacturing and recycling processes. The structures of the glasses differ from the standard soda-lime and borosilicate glasses, leading to a different mechanical behaviour. For instance, an anisotropic structure, which could exhibit a better mechanical performance than standard glasses. Furthermore, these new compositions incorporate up to 35% of slag and fly ash in their formulas. The valorization of these by-products that would otherwise have been previously discarded reduces costs and gas emission. The developed compositions have high water resistance, amorphous structure proved by x-ray diffraction and indentation toughness comparable to a standard soda-lime glass. The coloration of the samples varies depending on the composition and, for the samples containing slag, depending on the melting temperature. In this case, melting at higher temperatures allows the production of colorless glass. The color of the glasses is mainly influenced by the presence of sulfur and iron oxide. In conclusion, this thesis describes the development of new glass compositions containing fly ash and slag. The focus of the work is on the improvement of the properties and a comparison of performance of these new compositions with the glasses currently used in building engineering. The promising results point to the possibility of expansion of the current applications of glass.

The fracture toughness of three new compositional variants of the Zr-Ti-Be-LTM (Late Transition Metal) family of bulk metallic glasses (BMG's) are studied in the as-cast and annealed condition. Quaternary Zr-Ti-Cu-Be alloys consistently had linear elastic fracture toughness values greater than 80 MPa∙m1/2, while Vitreloy 1, a Zr-Ti-Cu-Ni-Be alloy, had an average fracture toughness of 48.5 MPa∙m1/2 with a large amount of scatter. The addition of iron to Vitreloy 1 reduced the fracture toughness to 25 MPa∙m1/2. The Zr-Ti-Cu-Be alloy, having fracture toughness KQ = 85 MPa∙m1/2 as cast, was annealed at various time/temperature combinations. When the alloy was annealed 50C below Tg, the fracture toughness dropped to 6 MPa∙m1/2, while DSC and X-ray showed the alloy to still be amorphous. Fracture surfaces were analyzed using scanning electron microscopy. The tougher samples have shown evidence of highly jagged patterns at the beginning stage of crack propagation, and the length scale and roughness of this jagged pattern correlate well with the measured fracture toughness values. These jagged patterns, the main source of energy dissipation in the sample, are attributed to the formation of shear bands inside the sample. This observation provides a strong evidence of significant “plastic zone” screening at the crack tip. Unlike the unstable fracture behavior of monolithic BMG's, ductile phase containing in-situ BMG composite shows stable crack growth behavior. Application of ductile BMG as a matrix for an in-situ composite with controlled microstructural characteristic length scales maximizes the toughening effect. In order to characterize this highly toughened BMG composite, the elastic-plastic fracture mechanics concept is introduced and the J-parameter is evaluated. A novel thermoplastic bonding concept is demonstrated based on the unique rheological behavior and pattern-replication ability of bulk metallic glass forming liquids. In this approach, the bulk metallic glass is heated above Tg to the “supercooled liquid” region while a small normal force is applied to the joint. This results in liquid reflow, wetting and a strong bond. Complete wetting between copper substrates and a layer of platinum based bulk metallic glass leads to an atomistically intimate void-free interface.

利用强流脉冲离子束(High Intensity Pulsed Ion Beam，HIPIB) 模拟核聚变装置中的瞬态高热负荷环境，离子束成分为Cn+(70%) 和H+(30%)、加速电压为250 kV，研究金属玻璃Zr53Al23.5Cu5.9Co17.6 和金属W在不同参数的HIPIB 辐照下结构和性能的变化规律以及损伤行为。XRD显示辐照后金属玻璃均保持非晶相为主要结构，金属W中有应力产生。SEM观察在辐照次数为3 和10 次时金属玻璃和金属W表面都没有明显的辐照损伤现象；当辐照次数增加到100 和300 次后，金属玻璃表面出现了花瓣状形貌和小球，金属W表面则出现了裂纹。纳米压痕仪测量辐照后金属玻璃的表面纳米硬度随辐照次数的增加逐渐降低。Zr 基金属玻璃具有较好的耐辐照性能，对HIPIB 辐照时产生强的热应力的缓冲能力比金属W好. High intensity pulsed ion beam(HIPIB) technology was used for simulating the transient heat load conditions of fusion reactor. The ion beam was mainly composed of Cn+(70%) and H+(30%) at an acceleration voltage of 250 kV. We investigated the changing rule of the structure and performance and damaged behavior of metallic glassZr53Al23.5Cu5.9Co17.6 and W metal under different number of pulses. XRD analysis showed that the metallic glass remained making amorphous phase as its main structure after HIPIB irradiation, while stress were produced in W metal. SEM analysis concluded that there was no apparent irradiation damage on the surface of metallic glass and W metal when the irradiation frequency was 3 and 10 times. While the irradiation frequency increased to 100 and 300 times, “petal”-shaped and balls appeared on the surface of metallic glass, and cracks appeared on the surface of W. Nanoindentor showed that nano-hardness for the surface of metallic glass after irradiation reduced gradually with the increase of the frequency of irradiation. Zr-based metallic glass had a better resistance under HIPIB irradiation. The buffering capacity of Zr-based metallic glass in connection with HIPIB irradiation-induced thermal stress is superior to W metal.

In this paper, we design a method that uses mechanical attrition to apply the electroless plating on the alloy surface, and compare the effect of electroless plating with that of traditional electroless plating. Based on the comparison results, we study the effects of mechanical attrition on the properties of electroless alloy plating during the electroless Ni-P plating. The results show that the mechanical attrition changes the growth pattern of Ni and P atoms in the traditional electroless plating. The resulting impact causes more energy to be transferred to the surface of the coating and brings plastic changes to the surface. The increase of the ion transport rate in the solution helps improve the uniformity of the coating. After mechanical attrition, the coating shows a very smooth and flat surface, indicating that this method effectively increases the coating density and at the same time saves a lot of coating resources. Mechanical attrition reduces the amorphism of the electroless coating so that the coating achieves the amorphous conversion from high to low energy. It can also make the zinc alloy coating harder and more resistant to corrosion. The surface of the magnesium alloy shows “cauliflower-like” structure. The “cauliflower” structure on the traditional electroless coating is not uniform, while the surface structure after the mechanical attrition is relatively smooth and flat, with tighter particle binding and no obvious pores. Amorphous Ni-P coating has an unstable mechanical shape in high temperature. Using the traditional chemical plating to coat the magnesium and zinc alloy can easily cause the coating to peel off or fail, while in the mechanical attrition method, the glass balls continuously impact the coating, increasing the atomic energy in the coating and inhibiting the galvanic corrosion between the coating and the magnesium alloy.

The local solid-particle volume fraction distributions were studied in a plexiglas rectangular CFB cold model with the size of 0.35 m ×0.48 m×4.9 m by using a reflective-type fiber-optic particle concentration probe(PC6D) in order to analyze the effects of the geometry structure on the gas-solid flow properties.The transparent glass bead with 366.2 μm diameter was used as bed materials during the experiment.Time series analysis and numerical interpolation methods were adopted to analyze the experimental data.Results showed that: in transition region,the expanding cross-section of wear wall structure significantly affected the gas-solid flow and the radial distribution of solid volume fraction was asymmetry;the local solid volume fraction near the wear wall was higher than the solid volume fraction near the front wall.In the dilute region,the offset-exit and the corner effect induced the defluxion of the particles movement and the core-annular distribution was broken.Time series analysis of the transient signals indicated that the two-phase structure in the bottom was unstable,and in the transition region the solids fluctuation was acute near the boundary between the core and annular section.